reliability: eprintln! panic on failed stderr write

[dean0x]

Location: crates/mds-cli/src/output.rs:513

What: eprintln! panics with 'failed printing to stderr' if the write fails (e.g., EPIPE when stdout is closed).

Why deferred: This is a pre-existing behavior pattern — every eprintln! site on main already has this property. Not a regression introduced by PR #253. However, it's worth documenting and potentially hardening in a dedicated pass.

Source review: .devflow/docs/reviews/fix-esc-injection-176/2026-07-25_1625 (reliability-6)

Acceptance Criteria:

• Audit all eprintln! sites in the crate
• Determine if EPIPE should be caught and silently ignored (common pattern)
• Consider using writeln! with explicit error handling where appropriate
• Add tests for stderr write failures if adding error handling

Note: This affects the watch command most directly. The Linux BrokenPipe stdin-test trap is a known pattern; verify behavior before adding error handling.